The invention relates to a method of determining scaling factors for fractal image coding, in which image areas of one or more images are searched for image coding, which image areas are imageable on other image areas with a minimal deviation while using the scaling factors and a corresponding geometric scaling.
In fractal image coding, as described, for example in the article "Fractal Image Coding and Magnification using Invariant Moments" by D. Gotting, A. Ibenthal and R. Grigat, Nato Advance Study Institute on Fractal Image Encoding and Analysis, Trondheim, 1995, an image coding of the contents of the image is performed by dividing the image into range blocks which do not overlap and represent the complete image contents. Furthermore, the image is divided into domain blocks which comprise parts of the image contents, preferably also in a transformed form. For each range block, that domain block is searched which is imageable on the relevant range block with the smallest deviation as far as image contents are concerned. The domain blocks comprise the image contents of the original image generally in a reduced form. A factor of 2 is customary. Although this factor has proved to be favorable for implementing the method, it may not always be the optimum factor.
For an optimum coding it is, however, advantageous to find the optimum reduction factor of the image contents in the domain blocks. Prior-art methods which would provide this possibility are not known.
In the prior art, the only possibility is to try out several reduction factors for the image contents in the domain blocks by performing the complete fractal image coding at different scaling factors and by subsequently checking the result on quality. It will be evident that this procedure leads to elaborate computations because it requires an image to be encoded many times to yield the optimum coding.